Joint arthroplasty is a well known surgical procedure by which a diseased and/or damaged natural joint is replaced by a prosthetic joint. Joint arthroplasty is commonly performed for hips, knees, elbows, and other joints. A hip arthroplasty includes the insertion of a prosthetic femoral stem component into the medullary canal of the femur. A ball or head is affixed to an end of the stem for articulation within a natural acetabulum or prosthetic acetabular component in the case of a total hip arthroplasty.
It is important that the femoral stem be securely positioned within the femur so as to achieve adequate initial fixation, as well to promote long term stability of the implant. Femoral components can have various design characteristics to provide optimal fixation properties, such as surface features for encouraging bony ingrowth, tailored flexibilities for reducing stress shielding, and particular surface properties for maximizing or minimizing adhesion to cement. While such femoral components may extend the useful life of the implant, a surgical revision of the prosthesis may become necessary after an extended period of time.
One problem associated with the revision of a femoral component is the difficulty of implanting a revision femoral component along the same longitudinal axis as the primary or original implant. It is desirable to implant the revision femoral component along the primary axis to emulate anatomical joint loading characteristics. The difficulty in implanting the revision prosthesis along the primary axis is generally attributable to bone loss on the posterior proximal portion of the femur. For example, if a revision femoral component having a symmetric proximal region is to be implanted, the region of proximal bone loss may prevent adequate fixation of the implant in the medullary canal. More particularly, there will be a gap between the implant and the bone which may result in deficient fixation of the femoral component in the proximal region of the femur. To eliminate the gap, a surgeon may attempt a bone graft to replace the lost bone. However, bone grafts can be time consuming and may not ultimately be successful.
Alternatively, a surgeon may implant a revision component that is larger than the original component so as to make up for the bone loss. However, the medullary canal must be reamed to remove additional material to accommodate the larger implant. Generally, the canal is reamed along an axis that is offset from the primary axis to compensate for the proximal bone loss. The offset results in a tendency for the revision component to twist under load since it is displaced from longitudinal axis of the femur, i.e., the primary axis.
Instead of a significantly larger revision component, a custom implant having a geometry adapted to compensate for the proximal bone loss can be implanted. However, the availability of custom implants may be limited. Furthermore, a large inventory of relatively costly components may need to be maintained.
A further option includes the use of a sleeve on a proximal end of a femoral component. However, conventional sleeves have a center that is offset from the centerline of the medullary canal. The offset center point results in misalignment of the revision femoral component with respect to the primary axis so as to provide less than optimal joint loading characteristics. Such displacement of the revision component from the primary axis results in a tendency of the implant to shift in position.
It would, therefore, be desirable to provide a sleeve for use with a revision prosthetic component that compensates for bone loss such that after implantation a longitudinal axis of the revision prosthetic component is coincident with the primary axis.